The present invention relates to on-board entertainment units and more particularly to motors for the deployment and retraction of the overhead monitor units.
Commercial airlines continuously try to make air travel as enjoyable as possible. One of such efforts is directed at providing in-flight entertainment (xe2x80x9cIFExe2x80x9d) for passengers individually or as a group broadcast. IFE is conventionally provided by installing liquid-crystal displays (xe2x80x9cLCDxe2x80x9d) for passengers throughout the cabin, either individual or by sections. The individual LCDs allow passengers to watch movies, play video games, do in-flight shopping or simply stay informed. Overhead LCDs are scattered throughout the cabin to provide flight status or news broadcast, since the overhead display of information does not require passengers to retrieve or activate their individual LCDs.
FIG. 1 illustrates a simplified diagram of an overhead LCD in a deployed mode. The LCD 100, shown deployed out of the cavity 110, which is typically built in the overhead storage compartment of an airplane cabin. The LCD 100 is deployed by a motor 120, e.g. direct current (xe2x80x9cDCxe2x80x9d) motor, through its control circuitry 125. When the motor 120 is activated for deployment by the flight attendant, the motor rotates to cause the linkage 135 to push the LCD 100 into a vertical, viewable position.
Under normal circumstances, the LCD 100 can be retracted through the motor 120 for stowage back to the cavity 110. However, for safety reasons, the Federal Aviation Administration (xe2x80x9cFAAxe2x80x9d) regulations mandate that the LCD be retracted even when there is power outage, since the passengers may hit the LCD in case of unexpected turbulence. In some commercial airlines, the LCDs are installed directly above passengers"" heads such that their deployment directly gets in the way when passengers stand up.
To address the FAA""s mandate of auto-retraction, the conventional approach has been to use a return coil spring 130. When the motor 120 deploys the LCD 100, the return spring 130 is energized such that when there is power outage, the springs 130 can retract the LCD by releasing its stored energy.
FIG. 2 shows a simplified diagram of a conventional motor 220 with the return coil spring 231 in a housing 230. Note that one end of the return spring 231 is attached to the motor shaft at 233, while the other end of the spring is attached to the housing at 232. Thus, as the motor shaft rotates to turn the linkage 235 during deployment, the spring is energized.
As with any mechanical and moving parts, there are problems associated with this approach. First, a spring has a limited life cycle such that after about 2000 uses, the spring needs to be replaced, or at least inspected. And replacing the spring is a tedious and labor intensive task, since one end of the spring is attached to the shaft of the motor and the other end is attached to the housing.
Further, if the motion of retraction is intervened externally, e.g. by a child""s hand, the energy previously stored in the spring may cause injury to the child""s hand. If the spring is broken, the LCD ends up being stuck in midway, which creates a safety problem in the event of strong turbulence.
In addition to the airline industry, other means of transportation may also encounter this power-off retraction problem.
Therefore, it is desirable to retract the LCD in case of power outage on the airplane in a consistent and reliable manner.
It is also desirable to ensure that the LCD is retracted even after the motion is intervened by external forces such as a passenger""s hand.
A retractor device for on-board LCD is disclosed. The retractor device uses capacitors as a storage device to provide electrical energy to drive the retractor motor in the reverse direction in the event of power outage. Under normal operating conditions, the deployment and retraction of the LCD is performed by the motor, with its polarity switched by a relay. At the same time, a storage capacitor is charged up. In the event of power outage while the LCD is in a deployed mode, the energy stored by the capacitor is discharged to drive the motor""s retraction mechanism. Blocking devices, such as diodes, may be used to ensure that the discharge path of the storage capacitor goes toward the motor.
The retractor device may further include a secondary capacitor to store electrical energy to be discharged following the discharge of the primary capacitor. By using a damping resistor to cause a slower discharge, the secondary capacitor will ensure that retraction be continued despite any intervention externally. Additional isolation devices, such as diodes, are implemented to prevent the discharge of the primary capacitor into the secondary loop, and vice versa. A voltage maintenance loop, including a diode and a single source power supply, may be included to ensure that the primary storage capacitor is fully charged at all time.